One of the most curious of these old medical (or perhaps I should say surgical) superstitions was that relating to the Powder of Sympathy, a remedy (?) chiefly remembered in connection with the name of Sir KENELM DIGBY (1603-1665), though he was probably not the first to employ it. The Powder itself, which was used as a cure for wounds, was, in fact, nothing else than common vitriol,(1) though an improved and more elegant form (if one may so describe it) was composed of vitriol desiccated by the sun's rays, mixed with _gum tragacanth_. It was in the application of the Powder that the remedy was peculiar. It was not, as one might expect, applied to the wound itself, but any article that might have blood from the wound upon it was either sprinkled with the Powder or else placed in a basin of water in which the Powder had been dissolved, and maintained at a temperate heat. Meanwhile, the wound was kept clean and cool. (1) Green vitriol, ferrous sulphate heptahydrate, a compound of iron, sulphur, and oxygen, crystallised with seven molecules of water, represented by the formula FeSO4<.>7H2O. On exposure to the air it loses water, and is gradually converted into basic ferric sulphate. For long, green vitriol was confused with blue vitriol, which generally occurs as an impurity in crude green vitriol. Blue vitriol is copper sulphate pentahydrate, CuSO4<.>5H2O. Sir KENELM DIGBY appears to have delivered a discourse dealing with the famous Powder before a learned assembly at Montpellier in France; at least a work purporting to be a translation of such a discourse was published in 1658,(1) and further editions appeared in 1660 and 1664. KENELM was a son of the Sir EVERARD DIGBY (1578-1606) who was executed for his share in the Gunpowder Plot. In spite of this fact, however, JAMES I. appears to have regarded him with favour. He was a man of romantic temperament, possessed of charming manners, considerable learning, and even greater credulity. His contemporaries seem to have differed in their opinions concerning him. EVELYN (1620-1706), the diarist, after inspecting his chemical laboratory, rather harshly speaks of him as "an errant mountebank". Elsewhere he well refers to him as "a teller of strange things"--this was on the occasion of DIGBY'S relating a story of a lady who had such an aversion to roses that one laid on her cheek produced a blister! (1) _A late Discourse... by Sir_ KENELM DIGBY, _Kt.&c. Touching the Cure of Wounds by the Powder of Sympathy...rendered... out of French into English by_ R. WHITE, Gent. (1658). This is entitled the second edition, but appears to have been the first.